Continue processing even if terminfo database couldn't be found (#673)

Fix #447 #543

This problem occurs when Fiddle can be loaded, curses can be loaded, and TERM is not registered in Terminfo.
It should also occur at hardcopy terminals and when Terminfo information is low, but no such reports have been received.

Reline should not abort the process because of missing Terminfo.
Reline proceeds with `Reline::Terminfo.enabled? == false` when fiddle or curses cannot be loaded.
And does the same when Terminfo is present but TERM is not.
https://github.com/ruby/reline/blob/ebab2875f1226f877376558d8758bc0e2a1776c7/lib/reline/terminfo.rb#L156-L160

You can check the operation with `TERM=foo bundle exec bin/console`.

lib/reline/ansi.rb

@@ -315,7 +315,7 @@ def self.move_cursor_down(x)
   end
 
   def self.hide_cursor
-    if Reline::Terminfo.enabled?
+    if Reline::Terminfo.enabled? && Reline::Terminfo.term_supported?
       begin
         @@output.write Reline::Terminfo.tigetstr('civis')
       rescue Reline::Terminfo::TerminfoError
@@ -327,7 +327,7 @@ def self.hide_cursor
   end
 
   def self.show_cursor
-    if Reline::Terminfo.enabled?
+    if Reline::Terminfo.enabled? && Reline::Terminfo.term_supported?
       begin
         @@output.write Reline::Terminfo.tigetstr('cnorm')
       rescue Reline::Terminfo::TerminfoError

lib/reline/terminfo.rb

@@ -80,23 +80,11 @@ module Reline::Terminfo
   def self.setupterm(term, fildes)
     errret_int = Fiddle::Pointer.malloc(Fiddle::SIZEOF_INT)
     ret = @setupterm.(term, fildes, errret_int)
-    errret = errret_int[0, Fiddle::SIZEOF_INT].unpack1('i')
     case ret
     when 0 # OK
-      0
+      @term_supported = true
     when -1 # ERR
-      case errret
-      when 1
-        raise TerminfoError.new('The terminal is hardcopy, cannot be used for curses applications.')
-      when 0
-        raise TerminfoError.new('The terminal could not be found, or that it is a generic type, having too little information for curses applications to run.')
-      when -1
-        raise TerminfoError.new('The terminfo database could not be found.')
-      else # unknown
-        -1
-      end
-    else # unknown
-      -2
+      @term_supported = false
     end
   end
 
@@ -148,9 +136,14 @@ def self.tigetnum(capname)
     num
   end
 
+  # NOTE: This means Fiddle and curses are enabled.
   def self.enabled?
     true
   end
+
+  def self.term_supported?
+    @term_supported
+  end
 end if Reline::Terminfo.curses_dl
 
 module Reline::Terminfo

test/reline/test_ansi_with_terminfo.rb

@@ -109,4 +109,4 @@ def test_more_emacs
     assert_key_binding("\e ", :em_set_mark, [:emacs])
     assert_key_binding("\C-x\C-x", :em_exchange_mark, [:emacs])
   end
-end if Reline::Terminfo.enabled?
+end if Reline::Terminfo.enabled? && Reline::Terminfo.term_supported?

test/reline/test_terminfo.rb

@@ -58,4 +58,4 @@ def test_tigetnum_with_error
     assert_raise(Reline::Terminfo::TerminfoError) { Reline::Terminfo.tigetnum('unknown') }
     assert_raise(Reline::Terminfo::TerminfoError) { Reline::Terminfo.tigetnum(nil) }
   end
-end if Reline::Terminfo.enabled?
+end if Reline::Terminfo.enabled? && Reline::Terminfo.term_supported?